Substrate and assembly thereof with dielectric removal for increased post height

ABSTRACT

An interconnection substrate includes a plurality of electrically conductive elements of at least one wiring layer defining first and second lateral directions. Electrically conductive projections for bonding to electrically conductive contacts of at least one component external to the substrate, extend from the conductive elements above the at least one wiring layer. The conductive projections have end portions remote from the conductive elements and neck portions between the conductive elements and the end portions. The end portions have lower surfaces extending outwardly from the neck portions in at least one of the lateral directions. The substrate further includes a dielectric layer overlying the conductive elements and extending upwardly along the neck portions at least to the lower surfaces. At least portions of the dielectric layer between the conductive projections are recessed below a height of the lower surfaces.

BACKGROUND OF THE INVENTION

The present invention relates to the art of electronic packaging, andmore specifically to assemblies incorporating semiconductor chips and tomethods and components useful in making such assemblies.

Many electronic devices utilize semiconductor chips, commonly referredto as “integrated circuits” which incorporate numerous electronicelements. These chips are mounted on substrates which physically supportthe chips and electrically interconnect each chip with other elements ofthe circuit. The substrate may be a part of a discrete chip package usedto hold a single chip and equipped with terminals for interconnection toexternal circuit elements. Such substrates may be secured to an externalcircuit board or chassis. Alternatively, in a so-called “hybrid circuit”one or more chips are mounted directly to a substrate forming a circuitpanel arranged to interconnect the chips and the other circuit elementsmounted to the substrate. In either case, the chip must be securely heldon the substrate and must be provided with reliable electricalinterconnection to the substrate. The interconnection between the chipitself and its supporting substrate is commonly referred to as “firstlevel” assembly or chip interconnection, as distinguished from theinterconnection between the substrate and the larger elements of thecircuit, commonly referred to as a “second level” interconnection.

The structures utilized to provide the first level connection betweenthe chip and the substrate must accommodate all of the requiredelectrical interconnections to the chip. The number of connections toexternal circuit elements, commonly referred to as “input-output” or“I/O” connections, is determined by the structure and function of thechip. Advanced chips capable of performing numerous functions mayrequire substantial numbers of I/O connections.

First level interconnection structures connecting a chip to a substrateordinarily are subject to substantial strain caused by thermal cyclingas temperatures within the device change during operation. Theelectrical power dissipated within the chip tends to heat the chip andsubstrate, so that the temperatures of the chip and substrate rise eachtime the device is turned on and fall each time the device is turnedoff. As the chip and the substrate ordinarily are formed from differentmaterials having different coefficients of thermal expansion, the chipand substrate ordinarily expand and contract by different amounts. Thiscauses the electrical contacts on the chip to move relative to theelectrical contact pads on the substrate as the temperature of the chipand substrate changes. This relative movement deforms the electricalinterconnections between the chip and substrate and places them undermechanical stress. These stresses are applied repeatedly with repeatedoperation of the device, and can cause breakage of the electricalinterconnections. Thermal cycling stresses may occur even where the chipand substrate are formed from like materials having similar coefficientsof thermal expansion, because the temperature of the chip may increasemore rapidly than the temperature of the substrate when power is firstapplied to the chip.

In what is known as flip-chip bonding, contacts on the front surface ofthe chip are typically provided with bumps of solder. The substrate hascontact pads arranged in an array corresponding to the array of contactson the chip. The chip, with the solder bumps, is inverted so that itsfront surface faces toward the top surface of the substrate, with eachcontact and solder bump on the chip being positioned on the appropriatecontact pad of the substrate. The assembly is then heated so as toliquify the solder and bond each contact on the chip to the confrontingcontact pad of the substrate. Because the flip-chip arrangement does notrequire leads arranged in a fan-out pattern, it provides a compactassembly. The area of the substrate occupied by the contact pads can beapproximately the same size as the chip itself. Moreover, the flip-chipbonding approach is not limited to contacts on the periphery of thechip. Rather, the contacts on the chip may be arranged in a so-called“area array” covering substantially the entire front face of the chip.Flip-chip bonding therefore is well suited to use with chips havinglarge numbers of I/O contacts. Flip-chip structures using relativelysmall pillars or post structures on one or more of the chip or thesubstrate have been used to create a more robust and easy-to-assemblypackage. However, there are still size limitations regarding flip-chip,even with pillar or post structures because such bonding ordinarilyrequires that the contacts on the chip be arranged in an area array toprovide adequate spacing for the solder bumps. Accordingly, flip-chipbonding normally cannot be applied to chips having rows ofclosely-spaced contacts, particularly when a distance is desired betweenthe front face of the chip and the substrate that is greater than thepitch of the chip.

SUMMARY OF THE INVENTION

An embodiment of the present disclosure relates to an interconnectionsubstrate. The substrate includes a plurality of electrically conductiveelements of at least one wiring layer defining first and second lateraldirections. Electrically conductive projections for bonding toelectrically conductive contacts of at least one component external tothe substrate, extend from the conductive elements above the at leastone wiring layer. The conductive projections have end portions remotefrom the conductive elements and neck portions between the conductiveelements and the end portions. The end portions have lower surfacesextending outwardly from the neck portions in at least one of thelateral directions. The substrate further includes a dielectric layeroverlying the conductive elements and extending upwardly along the neckportions at least to the lower surfaces. At least portions of thedielectric layer between the conductive projections are recessed below aheight of the lower surfaces.

The dielectric layer can be in the form of a solder mask. The recessedportions of the dielectric layer can be recessed at a distance of atleast five microns below the lower surfaces of the conductiveprojections. The dielectric layer can fully cover the neck portions. Thedielectric layer can fully cover the lower surfaces of the conductiveprojections or the dielectric layer can only partially cover the lowersurfaces of the conductive projections.

The conductive projections can include a metal such as copper, copperalloy, aluminum, nickel, and gold or combinations thereof. Solder can bejoined to at least the end portions of the conductive projections. Theend portions of the projections can have end surfaces remote from thelower surfaces and edge surfaces extending between the lower surfacesand the end surfaces.

The recessed portions of the dielectric layer can define a firstthickness above the wiring layer, and the end surfaces can be spacedabove the wiring layer at a first height that is between 20 and 70 μmgreater than the first thickness. Further, the conductive projectionscan be positioned along the wiring layer in an array in which they arespaced apart from each other at a pitch that is less than 200 μm. Therecessed portions can define a first thickness above the wiring layersuch that the end surfaces are spaced above the wiring layer at a firstheight that is at least 20 μm greater than the first thickness. Therecessed portions can define recessed surfaces, and the lower surfacesof the end portions can be positioned above the recessed surfaces at asecond height of at least 5 μm.

The substrate can further include a sheet like polymeric dielectricelement, and the conductive elements can extend along the dielectricelement. An element of the substrate, such as the dielectric layer, canhave a CTE less than 8 ppm/° C. Such an element can be made from atleast one of semiconductor, glass, or ceramic material.

The substrate can further include solder balls extending along at leastthe end portions of the conductive projections. The solder balls candefine lower edges along the conductive projections that are spacedapart from the recessed portions by portions of the solder resist layer.A microelectronic assembly can include such a substrate in combinationwith a microelectronic element having a front face with contacts exposedthereon and a back face spaced apart from the front face. The first faceof the microelectronic element can face the solder resist layer and thesolder balls can be joined to respective ones of the contacts of themicroelectronic element. Such an assembly can also include an underfilllayer disposed between the front face of the microelectronic element andthe substrate. The underfill layer can substantially surround edgesurfaces of the solder balls and can extend along the recessed portionsof the dielectric layer. The front face of the microelectronic elementcan be spaced apart from the recessed portions of the solder resistlayer at a first distance, and the solder balls can define portions of asphere having diameters that are less than the first distance. Such amicroelectronic assembly can be used in diverse electronic systems withone or more other electronic components electrically connected to themicroelectronic assembly.

An interconnection substrate according to another embodiment can includea plurality of electrically conductive elements of at least one wiringlayer defining first and second lateral directions and electricallyconductive projections having bonding surfaces for bonding toelectrically conductive contacts of at least one component external tothe substrate. The conductive projections extend from the conductiveelements above the at least one wiring layer and the conductiveprojections have concave edge surfaces extending inwardly and downwardlyfrom the bonding surfaces towards the conductive elements. The substratealso includes a dielectric layer overlying the conductive elements andextending along the concave edge surfaces, the dielectric layer betweenthe conductive projections is recessed below a height of the bondingsurfaces.

The bonding surfaces can meet the concave edge surfaces at a boundary,and the bonding surfaces and the concave edge surfaces together can forma continuous edge surface that changes direction abruptly at theboundary. Respective portions of the dielectric layer can extend alongthe concave edge surfaces to top edges near the boundary. The bondingsurfaces can be convex. Portions of the dielectric layer can extendalong the concave edge surfaces of the conductive projections to defineconcave edge surfaces of the dielectric layer portions.

Another embodiment of the present disclosure relates to a method formaking a microelectronic substrate. The method includes forming adielectric layer on an in-process unit including a wiring layer having aplurality of conductive elements extending in first and second lateraldirections and a plurality of conductive projections extending away fromthe elements above the wiring layer. The conductive projections have endportions remote from the conductive elements and neck portionssupporting the end portions between the conductive elements and the endportions. The end portions have lower surfaces extending outwardly fromthe neck portion in at least one of the lateral directions. Thedielectric layer is formed on the neck portions and at least up to thelower surfaces. Portions of the dielectric layer are then removed toform recessed portions between the projections.

The step of removing portions of the dielectric layer can be carried outsuch that portions of the dielectric layer remain extending along theneck portions and contacting at least the lower surfaces. The dielectriclayer can be a solder resist layer.

The step of removing portions of the dielectric layer can be carried outby a wet-blasting process. The wet-blasting process can be such that amixture of abrasive particles in a liquid medium is directed towardselected areas of the dielectric layer. The abrasive particles can havea diameter of at least about 5 μm. The liquid medium can be a liquidhaving chemical etching properties. The wet-blasting process can includecreating a directed flow of the mixture at a predetermined flow rate andpassing the substrate through the directed flow at a predeterminedvelocity a predetermined number of times. The wet-blasting process candeform the end portions of the projections to define convex end surfacesthereon.

The neck portions of the projections can be formed before forming thedielectric layer, and the end portions of the projections can be formedafter forming the solder resist layer and before removing portions ofthe solder resist layer.

The method can further include the step of depositing solder balls overat least the end portions of the projections. The solder balls can bespaced apart from the recessed portions of the solder resist layer byportions of solder resist layer extending along the neck portions. Amethod for making a microelectronic assembly can include making amicroelectronic substrate by the above method and mounting amicroelectronic element on the substrate. The microelectronic elementcan include a front surface having contacts thereon and a rear surfacespaced apart from and substantially parallel to the front surface. Themicroelectronic element can be mounted to the substrate by joining thecontacts to respective ones of the solder balls.

An alternative embodiment of a method for making a microelectronicsubstrate can include forming a dielectric layer on an in-process unitincluding a wiring layer having a plurality of conductive elementsextending in first and second lateral directions and a plurality ofconductive projections extending away from the elements above the wiringlayer. The electrically conductive projections can have bonding surfacesfor bonding to electrically conductive contacts of at least onecomponent external to the substrate. The conductive projections can haveconcave edge surfaces extending inwardly and downwardly from the bondingsurfaces toward the conductive elements, and the dielectric layer canoverlie the conductive elements and extend along the concave edgesurfaces. Portions of the dielectric layer are then removed to formrecessed portions between the projections. The step of removing portionsof the dielectric layer can be carried out such that portions of thedielectric layer remain extending along the concave edge surfaces to aboundary formed between the edge surface and the bonding surface.Removing portions of the dielectric layer can further be carried out bya wet-blasting process. The wet-blasting process can deform the bondingsurfaces the projections to define convex surfaces thereon. Thewet-blasting process can further deform the bonding surfaces such that aperiphery of the bonding surface widens along at least a portionthereof.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A shows a portion of a connection substrate according to anembodiment of the present disclosure;

FIG. 1B is a top plan view of a portion of the connection substrate ofFIG. 1;

FIG. 2 shows a portion of a microelectronic package including theconnection substrate of FIG. 1;

FIG. 3 shows an alternative embodiment of a connection substrate;

FIGS. 4-8 show a connection substrate such as that of FIG. 1 duringvarious stages of a method of fabrication thereof;

FIG. 9 shows a portion of a connection substrate according to analternative embodiment of the present disclosure;

FIG. 10 shows a portion of the connection substrate of FIG. 9 having abonding element joined thereto;

FIG. 11 shows a portion of an alternative connection substrate;

FIGS. 12-14 show a connection substrate, such as that of FIG. 9 duringvarious stages of a method of fabrication thereof;

FIG. 15 shows a microelectronic assembly including a substrate similarto that of FIG. 1; and

FIG. 16 shows an electronic system including a microelectronic assemblyhaving a substrate similar to that of FIG. 15.

DETAILED DESCRIPTION

Turning now to the drawings, where similar numeric references are usedto indicate corresponding features, FIG. 1 shows a portion of asubstrate 10 according to an embodiment of the present disclosure.Substrate 10 includes a wiring layer 11 with conductive features formedtherein which can be used for electrical connections through and withinsubstrate 10. These conductive features can include conductive pads 14and traces 12, which can be electrically connected with conductive pads14. A dielectric layer 40 overlies wiring layer 11 and gives supportthereto. Dielectric layer 40 can be structured such that wiring layer 11can extend along a substantially planar surface thereof and can overlysuch a surface. In one embodiment, wiring layer 11 can be partially orfully embedded within dielectric layer 40.

A conductive projection 18 of substrate 10 can extend in a directionabove a conductive feature of wiring layer 11, such as from surface 16of pad 14. Conductive projection 18 extends away from pad 14 and wiringlayer 11 to an end surface 34 that defines a height H1 for projection 18above wiring layer 11. Projection 18 includes a neck portion 20 and anend portion 30. Neck portion 20 is positioned adjacent to pad 14 andincludes base 22 of projection 18. End portion 30 includes a lowersurface 32 that is spaced away from base 22 by neck portion 20 such thatneck portion 20 extends to a corner 24 that substantially defines theupper end of neck portion 20. Neck edge surface 26 extends from base 22to corner 24 and defines an outer periphery of neck 20. The end portion30 has a surface 36 extending away from the lower surface 32. As seen inFIG. 1, end portion 30 may have an end surface 34 and an end edgesurface 36 extending between lower surface 32 and end surface 34 so asto define an outer periphery of end portion 30. Alternatively, the endportion 30 may present a continuous surface extending continuously fromthe lower surface 32 to end portion 30.

As shown in FIG. 1, at least part of neck portion 20 is narrower than atleast a part of end portion 30. In the embodiment shown, end portion 30is wider where end edge surface 36 meets lower surface 32 such thatlower surface 32 extends beyond neck edge surface 24 with lower surface32 substantially facing wiring layer 11. FIG. 1 shows neck portiontapering such that it is narrower at base 22 than at corner 24, howeverother arrangements are possible including one in which neck portion issubstantially of a uniform diameter or in which it tapers from a greaterwidth at base 22 to a lesser width at corner 24. End portion 24 cantaper from a greater thickness where end edge surface 36 meets lowersurface 32 to a lesser thickness at end surface 34, however end portion24 could be of a substantially uniform thickness.

The conductive elements of wiring layer 11, including traces 12 and pads14, as well as projections 18 can be formed from an electricallyconductive material. Such conductive materials can include copper, gold,nickel, aluminum, or various alloys comprising mixtures thereof.Additionally, the features within wiring layer 11 can be made of adifferent material than that of projections 18.

Dielectric layer 40 extends in lateral directions defined by wiringlayer 11 substantially over all of wiring layer 11. Dielectric layer 40has a thickness T1 over first portions 44 thereof such that at leastfirst surface portions 48 are substantially even with lower surfaces 32of posts 18. Dielectric layer 40 includes portions thereof that extendalong neck edge surfaces 26 and substantially surround neck portion 20.First surface portions 48 are formed on first portions 44 such that theyextend along lower surfaces 32 of end portions 30 with end edge surfaces36 and end surfaces 34 uncovered by dielectric layer 40.

Recessed portions 42 are included in dielectric layer 40 and definerecessed surfaces 46 therein that are spaced closer to wiring layer 11than first surface portions 48. Accordingly, within recessed portions42, dielectric layer has a thickness T2 that is less than thickness T1.In an embodiment, T2 is less than T1 by at least about 5 μm. Further,first portions 48 of dielectric layer. Dielectric edge surfaces 50extend at least partially between first surface portions 48 and recessedportions 42 and can define a boundary between first portions 44 andrecessed portions 42. Further, first portions 48 can be positionedgenerally beneath lower surfaces 32 or can be positioned generallybetween corresponding pads 14 and lower surfaces 32. A transitionsurface 52 can extend between recessed surfaces 46 and dielectric edgesurfaces 50 and can be positioned outside of lower surfaces 32. Byincluding recessed portions 42 with reduced thicknesses T2 in dielectriclayer 40, conductive projections have a height H2 above recessedportions that become effective projection heights above dielectric layer40. In an embodiment, H2 can be between about 20 and 70 μm. In anotherembodiment, H2 can be at least about 20 μm.

Projections 18 can be used to form connections in microelectronicpackages. For example, projections 18 can be used to connect amicroelectronic element 70, which can be in the form of a microchip orthe like, to substrate 10 such that projections 18 provide an electricconnection between microelectronic element 70 and wiring layer 11,thereby forming a microelectronic assembly 68. A portion of such amicroelectronic assembly 68 is shown in FIG. 2, but an embodiment of afull assembly including an enlarged substrate 60 according to anembodiment of the disclosure is shown in FIG. 14. As shown in FIG. 2,microelectronic element can include contact pads 72 thereon that areexposed on a front surface 74 thereof. Microelectronic element 70 can beflip-chip bonded to substrate 10 by solder balls bonded betweenrespective projections 18 and contact pads 72. In such a structure, agap G1 is formed between front face 74 of microelectronic element 70 andrecessed surfaces 46 of dielectric layer 40. An underfill layer 76 canbe between the front surface 74 of microelectronic element 70 andsubstrate 10 within gap G1. Underfill layer 76 can extend along portionsof surface 74 exposed between solder balls 74 as well as the edges ofsolder balls 54 and along dielectric edge surfaces 50 and along recessedsurfaces 44. Underfill layer 76 can be formed from a curable polymericmaterial.

Dielectric layer 40 can be formed from a solder mask layer such thatsolder balls 54, when formed on projections 18 or when re-flowed duringassembly, do not wick or otherwise contact or extend along substantialportions of dielectric edge surfaces 50 and remain out of contact withrecessed surfaces 46. In such an embodiment, solder balls 54 extend onlyalong end surfaces 34 and end edge surfaces 36. Accordingly, aconnection structure including a solder ball 54 having a diameter of D1can be formed that allows for a gap G1 that is greater than the gap G2which could be achieved in an arrangement (FIG. 3) in which surface 148of dielectric layer 40 has no recesses. Because solder tends to formsubstantially spherical edge surfaces when deposited or reflowed due tothe surface tension of the metal when melted, increasing post height hasresulted in a larger overall solder ball with a correspondinglyincreased diameter. However, as shown in FIG. 2, a post structure can beprovided with a greater effective height H2 than that of FIG. 3, whichcan result in a greater gap G1, compared to the gap G2 (FIG. 3) with asolder ball 54 that is of a comparable diameter D1. Accordingly,projections 18 can be spaced apart form each other at a pitch P1 (shownin FIG. 1B) that is comparable to the pitch allowed only by shorterprojections in the FIG. 3 arrangement. In an embodiment, the pitch P1can be less than about 200 μm.

As also shown in FIG. 2, substrate 10 can be in the form of a multilayersubstrate that includes, for example, a further dielectric layer 82beneath wiring layer 11 and dielectric layer 40. Dielectric 82 cansupport any additional wiring layers 62 having pads or traces or acombination thereof. Although only a single layer of traces 84 are shownin FIG. 2, a greater number of wiring layers of is possible. Such layerscan be connected by conductive vias 64 or the like, which are shown inFIG. 2 connecting wiring layer 62 to pads 14.

FIGS. 4-8 illustrate steps in forming a substrate 10 according to theembodiments shown in FIGS. 1 and 2. As shown in FIG. 4, an in-processunit 10′ is shown as a layer of dielectric material 40, which is can bea solder-mask layer, as described above. Wiring layer 11, includingconductive traces 12 and conductive pads 14 is formed extending along asurface of the dielectric layer 40. In-process unit 10′ can be formed,for example, by etching the features of wiring layer 11 from a layer ofmetal that is either formed on top of a carrier or on lower layers of amultilayer substrate, as described with respect to FIG. 2, although onlyin-process unit 10′ is illustrated herein. Alternatively, a similarwiring layer can be formed by etching a metal layer or by direct platingon a surface of a dielectric layer.

In FIG. 5, a plurality of holes 28 are formed in dielectric layer 40.Holes 28 can be formed by photo-etching using a mask or resist layer, orcan be formed by laser etching, chemical etching or the like. Holes 28are formed over pads 14 or otherwise in the desired location forconductive projections 18 to be formed later for electrical connectionto a feature above the resulting substrate 10. Holes 28 expose at leasta portion of pads 14 for access thereto.

In FIG. 6, a plating layer 38 is formed over the first surface 48′ ofdielectric layer 40 and within holes 28. Layer 38 can be formed byplating copper until the proper thickness is built up over surface 41and holes 28 are filled. Portions of layer 38 form neck portions 20within holes 28, including bases 22 along portions of layer 38 thatcontact and are bonded to pads 14. Neck edge surfaces 26 are formedalong the portions of dielectric layer 40 that define holes 28 such thatdielectric layer 40 extends along neck edge surfaces 26. A lower surface32′ of plating layer 38 is formed along first surface 48′″.

As shown in FIG. 7, plating layer 38 is then selectively etched, usingchemical etching or the like to form end portions 30′ for conductiveprojections 18. In the etching process areas of plating layer 38 areremoved outside of selected areas thereof that correspond to pads 14 andthe neck portions 20 formed thereon in the step shown in FIG. 6. Platinglayer 38 is removed in the selected areas such that surface 48′ ofdielectric layer is exposed between end portions 30′. Further, endportions 30′ are formed such that portions of surface 32′ of platinglayer 38 remain extending outward from neck edge surfaces 26 alongportions of surface 48′.

Recessed portions 42 are formed in dielectric layer 40 resulting in thestructure of FIG. 8. Recessed portions 42 are structurally describedabove with respect to FIG. 2, and, in one embodiment, can be formedusing a wet blasting process. Wet blasting is a mechanical etchingprocess that uses a high-pressure, focused liquid flow directed at thesubstrate 10′ to remove material therefrom. In a particular embodiment,the liquid medium can include an etchant which may help to etch orremove portions of the dielectric layer selectively relative to metalwhich is exposed to the flow. Wet-blasting can be performed in aselective manner such that the process reduces a thickness of thedielectric layer 40 selectively relative to the end portions 30 withoutrequiring the use of a mask layer or similar structure. Wet-blasting canalso be carried out after the application of a mask layer over, forexample, the ends 30 of projections 18 or over areas of the dielectriclayer 40 where recesses are not desired. Further, wet-blasting can becarried out in a non-selective manner over the entire substrate, relyingon the differences in hardness of the various structures to create thedesired structures. The wet-blasting process removes material in thearea of recessed portions 42 over time and is carried out until thedesired thickness T2 is reached for the areas of dielectric layer 40within recessed portions 42. During the wet blasting operation, endportions 30 can become deformed, including for example, rounding at theperiphery of end surface 34 or the like, or material can be removedtherefrom; however, such deformation can be less than that of dielectriclayer 40, leaving end portions 30 substantially intact. The portions ofdielectric layer 40 that are disposed beneath lower surfaces 32 aresubstantially protected from the wet blasting and are, accordingly, alsoleft surrounding neck portions 20.

Wet-blasting can be carried out, for example, using a slurry or mixtureof abrasive particles in a liquid medium. The abrasive particles can besimilar to those that can be used in sand blasting or bead blasting andcan have a diameter of at least about 5 μm. The liquid medium can bewater or can be a chemical or chemical mixture. Such chemicals ormixtures can include chemical etchants or solder mask strip chemicals.The liquid medium can also include additives for pH control or otherproperties. Sand blasting or bead blasting, with no liquid medium, canalso be used as alternatives to the wet-blasting process.

Depending upon the particle characteristics and density within themedium, the amount of time the substrate is exposed to the flow can beadjusted to attain the depth of recess desired. These parameters mayalso be adjusted to attain projections having a desired shape, e.g.,extent to which the end surfaces overhang the edge surfaces.

Portions of first surface 48 are also left extending along at least someof lower surfaces 32. This step also results in the formation ofdielectric edge surfaces 50 that extend beneath end edge surfaces 36.Recesses 42 can also be formed by other reductive processes, such asmechanical or chemical etching. A Saw or laser can be used to form therecesses between end portions by moving over the dielectric layer 40 intwo transverse directions over several passes through the desired areafor recesses 42. In this case, the recesses may not be aligned with theedges 36 of the end portions 30, but may instead be spaced aparttherefrom.

The substrate 10 formed by the described steps can then be used to forma packaged microelectronic element as shown in FIG. 2. An underfilllayer 76 can be formed between front surface 74 of microelectronicelement 70 and recessed surfaces 46 and surrounding solder balls 54 anddielectric edge surfaces 50. The wet blasting process can result in aroughness on surfaces 46 and 50 such that underfill adherence isimproved compared to that of, for example an un-blasted surface such assurface 48.

In a variation of the above embodiment, substrate 210 can haveconductive projections 218, as shown in FIGS. 9 and 10. Substrate 210includes conductive projections 218 having concave edge surfaces 226disposed between bases 220 and convex end surfaces 234. The concave edgesurfaces may extend continuously between the bases 220 and the endsurface 234. Edge surfaces 226 can be such that upper portions 232thereof extend outwardly and at least partially face toward wiring layer211. Dielectric layer 240 extends along edge surface 226, includingalong upper portion 232 thereof and includes recessed portions 242formed therein. Recessed portions 242 define recessed surfaces 246 alongbottom portions thereof wherein dielectric layer 40 has a thickness T2.First portions 244 of dielectric layer 240 are positioned at leastpartially below convex end surfaces 234 within the convex area definedby convex edge surfaces 236, including below the upper portion 236thereof. First portions 244 define dielectric edge surfaces 250 thatextend substantially downward from end surface 236 and transition torecessed surfaces 246.

As described above with respect to FIG. 2, dielectric layer 240 can bemade from a solder mask material such that solder balls 254 that areformed on projections 218 do not extend along dielectric edge surfaces250 and do not contact recessed surfaces 246. As shown in a comparisonof the embodiment of FIG. 10 to the prior-art structure depicted in FIG.11, a solder ball having a smaller diameter D2 can be formed overprojection 218 than over the projection 118 of the prior art because thesolder does not wick downward. Accordingly, multiple projections 218 canbe formed in an array having a smaller pitch than would be possible inthe structure shown in FIG. 11 of a projection having the same bight H3.

FIGS. 12-14 show substrate 210 in various forms during sequential stepsfor fabrication thereof. In FIG. 12, projections 218′ are formed on pads14 that are formed on a lower layer 60 that will form a multilayersubstrate structure, although other substrate arrangements for packagedmicroelectronic structures are possible. Projection 218′ is shown as anetch post formed from one layer of a tri-metal layer including anetch-stop layer 223, however, alternative structures can be used, suchas that shown for end portion 230 of projection 18 in FIG. 1. In anembodiment layer 60 can be a sheet-like polymeric element. In a furtherembodiment, layer 60 can be of a material having a low coefficient ofthermal expansion (“CTE”) such as of about 8 parts per million per ° C.(“PPM/° C.”) or less. Such materials can include certain types ofsemiconductor materials, glass, or ceramic.

In FIG. 13 dielectric layer 240′ is formed over layer 260 and over anyexposed portions of pad 14 and upward along edge surface 226 ofprojection 218′. End surface 234′ can be left exposed on surface 248′ ofdielectric layer. Subsequently a wet-blasting process, as described withrespect to FIG. 8 is applied to substrate 210′ to remove portions ofdielectric layer 240′ between projections 218′ and in the desired areafor recessed portions 242. Because the material of dielectric layer 240′is softer than the material of posts 218′, the wet-blasting processremoves material at a faster rate from dielectric layer 240′ than fromprojections 218′. Accordingly, as the process begins, portions of edgesurface 226′ can become exposed over dielectric layer 240′. The exposureof portions of edge surface 226′ can allow for deformation ofprojections 218′, including the formation of a convex shape for endsurface 234 and an increase in the degree of the concave shape for edgesurface 226 as upper portion 232 thereof is pushed outward in theexposed area thereof over dielectric layer 240. Some removal of materialfrom projections 218 can also occur during this process. As thewet-blasting process continues, upper portion 232 of edge surface canextend outwardly over a portion 244 of dielectric layer 240, furthershielding that portion 244 from further effects of wet-blasting.Accordingly, the structure of FIG. 14 can result in which portions ofdielectric layer 244 surround projections 18 beneath end surfaces 234and extending along edge surfaces 226.

The interconnection components described above can be utilized inconstruction of diverse electronic systems, as shown in FIG. 15. Forexample, a system 90 in accordance with a further embodiment of theinvention can include a microelectronic assembly 68, being a unit formedby assembly of a microelectronic element 70 on substrate 10, similar tothe microelectronic assembly 68 shown in FIG. 14 The embodiment shown,as well as other variations of the interconnection component orassemblies thereof, as described above can be used in conjunction withother electronic components 92 and 94. In the example depicted,component 92 can be a semiconductor chip or package or other assemblyincluding a semiconductor chip, whereas component 94 is a displayscreen, but any other components can be used. Of course, although onlytwo additional components are depicted in FIG. 15 for clarity ofillustration, the system may include any number of such components. In afurther variant, any number of microelectronic assemblies including amicroelectronic element and an interconnection component can be used.The microelectronic assembly and components 92 and 94 are mounted in acommon housing 91, schematically depicted in broken lines, and areelectrically interconnected with one another as necessary to form thedesired circuit. In the exemplary system shown, the system includes acircuit panel 96 such as a flexible printed circuit board, and thecircuit panel includes numerous conductors 98, of which only one isdepicted in FIG. 14, interconnecting the components with one another.However, this is merely exemplary; any suitable structure for makingelectrical connections can be used, including a number of traces thatcan be connected to or integral with contact pads or the like. Circuitpanel 96 can have contacts 52 thereon, and can connect tointerconnection component 2 using solder balls 32 or the like. Thehousing 91 is depicted as a portable housing of the type usable, forexample, in a cellular telephone or personal digital assistant, andscreen 94 is exposed at the surface of the housing. Where structure 90includes a light-sensitive element such as an imaging chip, a lens 99 orother optical device also may be provided for routing light to thestructure. Again, the simplified system 90 shown in FIG. 14 is merelyexemplary; other systems, including systems commonly regarded as fixedstructures, such as desktop computers, routers and the like can be madeusing the structures discussed above.

Although the invention herein has been described with reference toparticular embodiments, it is to be understood that these embodimentsare merely illustrative of the principles and applications of thepresent invention. It is therefore to be understood that numerousmodifications may be made to the illustrative embodiments and that otherarrangements may be devised without departing from the spirit and scopeof the present invention as defined by the appended claims.

1. An interconnection substrate, comprising: a plurality of electricallyconductive elements of at least one wiring layer defining first andsecond lateral directions; electrically conductive projections forbonding to electrically conductive contacts of at least one componentexternal to the substrate, the conductive projections extending from theconductive elements above the at least one wiring layer, the conductiveprojections having end portions remote from the conductive elements andneck portions between the conductive elements and the end portions, theend portions having lower surfaces extending outwardly from the neckportions in at least one of the lateral directions; and a dielectriclayer overlying the conductive elements and extending upwardly along theneck portions at least to the lower surfaces, at least portions of thedielectric layer between the conductive projections being recessed belowa height of the lower surfaces.
 2. The substrate of claim 1, wherein thedielectric layer is a solder mask.
 3. The substrate of claim 1, whereinthe recessed portions of the dielectric layer are recessed at a distanceof at least five microns below the lower surfaces of the conductiveprojections.
 4. The substrate of claim 1, wherein the dielectric layerfully covers the neck portions.
 5. The substrate of claim 1, wherein thedielectric layer only partially covers the lower surfaces of theconductive projections.
 6. The substrate of claim 1, wherein thedielectric layer fully covers the lower surfaces of the conductiveprojections.
 7. The substrate of claim 1, wherein the conductiveprojections consist essentially of at least metal selected from thegroup consisting of: copper, copper alloy, aluminum, nickel, and gold.8. The substrate of claim 7, further comprising solder joined to atleast the end portions of the conductive projections.
 9. The substrateof claim 1, further comprising a sheet-like polymeric dielectricelement, wherein the conductive elements extend along the dielectricelement.
 10. The substrate of claim 1, further comprising an elementhaving a CTE less than 8 ppm/° C., wherein the conductive elementsextend along the element.
 11. The substrate of claim 10, wherein theelement consists essentially of at least one of semiconductor, glass, orceramic material.
 12. The substrate of claim 1, wherein the end portionshave end surfaces remote from the lower surfaces and edge surfacesextending between the lower surfaces and the end surfaces.
 13. Thesubstrate of claim 12, wherein the recessed portions define a firstthickness above the wiring layer, wherein the end surfaces are spacedabove the wiring layer at a first height that is between 20 and 70 μmgreater than the first thickness, wherein the conductive projections arepositioned along the wiring layer in an array in which they are spacedapart from each other at a pitch that is less than 200 μm.
 14. Thesubstrate of claim 1, wherein the recessed portions define a firstthickness above the wiring layer, wherein the end surfaces are spacedabove the wiring layer at a first height that is at least 20 μm greaterthan the first thickness.
 15. The substrate of claim 1, wherein theconductive projections are positioned along the mask layer in an arrayin which they are spaced apart from each other at a pitch that is lessthan 200 μm.
 16. The substrate of claim 15, wherein the recessedportions define recessed surfaces, and wherein the lower surfaces arepositioned above the recessed surfaces at a second height of at least 5μm.
 17. The substrate of claim 1, further including solder ballsextending along at least the end portions of the conductive projections,and wherein the solder balls define lower edges along the conductiveprojections and spaced apart from the recessed portions by portions ofthe solder resist layer.
 18. A microelectronic assembly, comprising: thesubstrate of claim 17; and a microelectronic element having a front facewith contacts exposed thereon and a back face spaced apart from thefront face, wherein the first face of the microelectronic element facesthe solder resist layer and wherein the solder balls are joined torespective ones of the contacts of the microelectronic element.
 19. Theassembly of claim 18, further comprising an underfill layer disposedbetween the front face of the microelectronic element and the substrate,the underfill layer substantially surrounding edge surfaces of thesolder balls and extending along the recessed portions of the dielectriclayer.
 20. The microelectronic assembly of claim 18, wherein the frontface of the microelectronic element is spaced apart from the recessedportions of the solder resist layer at a first distance, and wherein thesolder balls define portions of a sphere having diameters that are lessthan the first distance.
 21. A system comprising: a microelectronicassembly according to claim 18 and one or more other electroniccomponents electrically connected to the microelectronic assembly. 22.An interconnection substrate, comprising: a plurality of electricallyconductive elements of at least one wiring layer defining first andsecond lateral directions; electrically conductive projections havingbonding surfaces for bonding to electrically conductive contacts of atleast one component external to the substrate, the conductiveprojections extending from the conductive elements above the at leastone wiring layer, the conductive projections having concave edgesurfaces extending inwardly and downwardly from the bonding surfacestowards the conductive elements; and a dielectric layer overlying theconductive elements and extending along the concave edge surfaces, thedielectric layer between the conductive projections being recessed belowa height of the bonding surfaces.
 23. The substrate of claim 22, whereinthe bonding surfaces meet the concave edge surfaces at a boundary, andwherein the bonding surfaces and the concave edge surfaces together forma continuous edge surface that changes direction abruptly at theboundary.
 24. The substrate of claim 23, wherein respective portions ofthe dielectric layer extend along the concave edge surfaces to top edgesnear the boundary.
 25. The substrate of claim 22, wherein the bondingsurfaces are convex.
 26. The substrate of claim 22, wherein portions ofthe dielectric layer extending along the concave edge surfaces of theconductive projections define concave edge surfaces of the dielectriclayer portions.
 27. A system comprising: a microelectronic assemblyaccording to claim 22 and one or more other electronic componentselectrically connected to the microelectronic assembly.
 28. A method formaking a microelectronic substrate, comprising the steps of: forming adielectric layer on an in-process unit including a wiring layer having aplurality of conductive elements extending in first and second lateraldirections and a plurality of conductive projections extending away fromthe elements above the wiring layer, the conductive projections havingend portions remote from the conductive elements and neck portionssupporting the end portions between the conductive elements and the endportions, the end portions having lower surfaces extending outwardlyfrom the neck portion in at least one of the lateral directions, thedielectric layer formed on the neck portions and at least up to thelower surfaces; and removing portions of the dielectric layer to formrecessed portions between the projections.
 29. The method of claim 28,wherein the step of removing portions of the dielectric layer is carriedout such that portions of the dielectric layer remain extending alongthe neck portions and contacting at least the lower surfaces.
 30. Themethod of claim 28, wherein the dielectric layer is a solder resistlayer.
 31. The method of claim 28, wherein the step of removing portionsof the dielectric layer is carried out by a wet-blasting process. 32.The method of claim 31, wherein the wet-blasting process directs amixture of abrasive particles in a liquid medium toward selected areasof the dielectric layer.
 33. The method of claim 32, wherein theabrasive particles have a diameter of at least about 5 μm.
 34. Themethod of claim 32, wherein the liquid medium is a liquid havingchemical etching properties.
 35. The method of claim 32 whereinwet-blasting process includes creating a directed flow of the mixture ata predetermined flow rate, and passing the substrate through thedirected flow at a predetermined velocity a predetermined number oftimes.
 36. The method of claim 31, wherein the wet-blasting processdeforms the end portions of the projections to define convex endsurfaces thereon.
 37. The method of claim 28, wherein the neck portionsof the projections are formed before forming the dielectric layer, andwherein the end portions of the projections are formed after forming thesolder resist layer and before removing portions of the solder resistlayer.
 38. The method of claim 28, further including the step ofdepositing solder balls over at least the end portions of theprojections, wherein the solder balls are spaced apart from the recessedportions of the solder resist layer by portions of solder resist layerextending along the neck portions.
 39. A method for making amicroelectronic assembly, comprising the steps of: making amicroelectronic substrate according to the method of claim 38; andmounting a microelectronic element on the substrate, the microelectronicelement including a front surface having contacts thereon and a rearsurface spaced apart from and substantially parallel to the frontsurface, the microelectronic element being mounted to the substrate byjoining the contacts to respective ones of the solder balls.
 40. Amethod for making a microelectronic substrate, comprising the steps of:forming a dielectric layer on an in-process unit including a wiringlayer having a plurality of conductive elements extending in first andsecond lateral directions and a plurality of conductive projectionsextending away from the elements above the wiring layer, theelectrically conductive projections having bonding surfaces for bondingto electrically conductive contacts of at least one component externalto the substrate, the conductive projections having concave edgesurfaces extending inwardly and downwardly from the bonding surfacestowards the conductive elements, the dielectric layer overlying theconductive elements and extending along the concave edge surfaces; andremoving portions of the dielectric layer to form recessed portionsbetween the projections.
 41. The method of claim 40, wherein the step ofremoving portions of the dielectric layer is carried out such thatportions of the dielectric layer remain extending along the concave edgesurfaces to a boundary formed between the edge surface and the bondingsurface.
 42. The method of claim 40, wherein the step of removingportions of the dielectric layer is carried out by a wet-blastingprocess.
 43. The method of claim 42, wherein the wet-blasting processdeforms the bonding surfaces the projections to define convex surfacesthereon.
 44. The method of claim 43, wherein the wet-blasting processfurther deforms the bonding surfaces such that a periphery of thebonding surface widens along at least a portion thereof.